Transcript document

Network Security Fundamentals
Chapter 6:
Securing Network
Transmission
Types of Attacks
• Packet sniffers
– Eavesdropping on network data
• Denial of Service (DoS)
– Misdirecting packets via router, switch
or hub
– Overwhelming devices with large
numbers of packets
TCP Session Hijacking
• Normal TCP/IP session
– Client initiates 3-way handshake with server
using SYN, ACK messages
• TCP session hijacking
– Attacker impersonates valid client
– Can be run in Unix environment, where
attacker spoofs messages from trusted host
– Can be run in environment where
authentication not required
TCP/IP Session Initiation
TCP Session Hijacking Attack
TCP SYN Flooding Attacks
• Half-open connections
– In SYN_RECV state, computers limit number
of connections that haven’t completed
handshake
• TCP SYN flooding attack
– Attacker initiates large number of open
requests (SYN packets) without completing
handshake, so B reaches limit and cannot
respond to more requests
Considerations for Designing
a Secure Infrastructure
• Decide what network traffic needs
securing
• Identify compatibility issues of operating
systems installed and applications running
on them
• Ensure hardware is secure
• Determine methods to use to secure data
that will be transmitted over network
Securely Transmitting Data
• When data needs to be securely
transmitted over network, to mitigate risk
of attack:
– Ensure data will not be read by unauthorized
individuals between you and source
– Verify/authenticate identity of people,
computers sending packets
– Verify data will not be tampered with during
transit
Defining Network Perimeters
• One way to secure network
– Isolate segments that have secure data transmission
requirements
• You can segment network at:
– Layer 3: Using routers, subnets
– Layer 2: Using switches, VLANs
• Network perimeter: Any point connecting internal
network to external network
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Screened subnets
DMZs
WAPs
VPN connections
Isolating Insecure Networks
Using Subnets
• Screened subnet
– Uses routers, firewalls to screen traffic
– Three main configurations
• Bastion host
• Three-pronged configuration
• Back-to-back configuration
Isolating Insecure Networks
Using Subnets
• Bastion host
– Acts as sole connection to Internet
– Two network adapters for:
• Internet network
• External network
– Can be single point of failure
Bastion Host
Isolating Insecure Networks
Using Subnets
• Three-pronged configuration
– Firewall system has three network
adapters, for:
• Internal network
• External/public network
• Screened subnet
– Allows hosts from both internal and
external networks to access resources
on screened subnet
Three-Pronged Configuration
Isolating Insecure Networks
Using Subnets
• Back-to-back configuration
– Screen subnet placed between two
firewalls
• Between subnet and Internet
• Between subnet and internal network
– Most secure configuration
Back-to-Back Configuration
Switches and VLANs
• Virtual LANs (VLANs)
– Created with switches
– Tag (VLAN ID) associates hosts in
VLAN
– Limits broadcast domain:
• All communication occurs through router
– Subject to VLAN hopping
• Attackers bypass VLAN boundary by
modifying VLAN ID
Using IP Addresses
and IP Packet Filtering
• Filtering: Added layer of protection
• IP address filtering
– Filtering traffic based on client’s IP address
– Two main options:
• Enabling all traffic except for IP address list
• Allow only IP addresses listed
• IP packet filtering
– Filter defined by protocols or ports
– Prevents specific packets from reaching
destined ports
IP Address Filtering in IIS
Data Transmission
Protection Protocols
• Protocols for protecting data when
transmitted, by:
– Authenticating
– Encrypting
– Ensuring integrity of data
• Data transmission protection protocols
include:
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SSL and TLS
IPsec
SMB Signing
SSH
SSL and TLS
• Provide session encryption and integrity
for client-server or server-server traffic
• Can provide client authentication through
X.509 certificates
• SSL: Two components
– SSL Handshake protocol: Sets up
cryptographic parameters
– SSL Record layer: Provides encryption
services
• TLS: Enhancement of SSL
SSL on a Network
The SSL Security Layer
SSL Handshake Protocol
ClientHello Message
ServerHello Message
IP Security (IPsec)
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Operates at Internet; application-independent
Optional with IPv4, required with IPv6
Used to secure traffic on LAN or VPN
Can be configured for:
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Confidentiality
Authentication
Data integrity
Packet filtering
Protection against data replay attacks
• Can be configured to use multiple security
algorithm options
IPsec on the Stack
IP Security (IPsec)
• Two major security mechanisms:
– Authentication header
• Protects integrity, authenticity only
– Encapsulating security payload (ESP)
• Can provide:
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Confidentiality
Data origin authenticity
Data integrity
Some replay protection
Limited traffic flow confidentiality
ESP
• ESP packet
– Header
• Security Parameters Index (SPI)
• Sequence number
– Payload data
– Trailer
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•
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Padding
Pad length
Next header
Authentication data
ESP packet
ESP
• ESP can operate in one of two
modes
– Transport mode
• Encapsulates upper-layer protocol frame
• Provides end-to-end protection
– Tunnel mode
• Original IP datagram encapsulated within
outer IP datagram (IP within IP)
• Provides gateway-to-gateway security
Transport Mode
Tunnel Mode
Security Associations (SA)
• Stores cryptographic data
– Algorithm, key, key lifetimes
– Enables system to generate, decrypt, verify
ESP packets
• Created in pairs
– Two SAs required for bidirectional
communication between two hosts
• Uniquely identified by:
– SPI (in AH and ESP headers)
– Destination IP address
– Security protocol (AH, ESP) identifier
Internet Key Exchange Protocol
(IKE; IKEv2)
• Alternative to manually creating SAs
• Provides for:
– Entity authentication
– Establishment of fresh shared secret, used to
derive additional keys
– Secure negotiation of all cryptographic
algorithms
• Authentication method, key exchange method,
encryption algorithms, hash algorithms
Configuring IPsec on
a Windows Network
• Windows built-in, basic IPsec policies
– Client (Respond Only)
– Server (Request Security)
– Server (Require Security)
• Can create custom IPsec policy with rules for:
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Filters, filter actions
Authentication (Kerberos v5, PKI, or preshared key)
Mode (tunnel or transport)
Network interface policy applies to
Means for exchanging keys over Internet using IKE
Default IPsec Policies On
A Windows 2003 Computer
Creating IPsec Rules On
Windows 2003 Computer
Server Message Block Signing
• Server Message Block (SMB) protocol
– Used when accessing files over network share on
Windows server
– By default, not secure
• SMB signing: Adds keyed hash to each SMB
packet
– Guards against man-in-middle, replay, session hijacking
attacks
– Does not provide confidentiality
– Enabled by default on Windows 2000 Server, XP, Server
2003
– If not enabled on client, client cannot access server with
enabled SMB signing
Allowing Connections from Clients That
Don’t Support SMB Signing
Secure Shell
• Secure Shell (SSH, SSHv2)
– Provides security for remote login programs
(Telnet, FTP)
– Uses public key encryption schemes to provide
data confidentiality and authentication
– Features include:
• Replaces conventional remote login programs (sftp,
sshd)
• Supports multiple encryption algorithms
• High-end security algorithms to detect identity
spoofing
• Authentication through RSA or DSA key pairs
Summary
• Types of attacks involving network traffic
include use of malicious packet sniffers;
DoS attacks; TCP session hijacking; and
TCP SYN flooding attacks.
• Considerations for designing secure
infrastructure include: Deciding what
network traffic needs securing; identifying
compatibility issues with operating system
and application software; securing
hardware; and determining methods to use
for securing data being transmitted.
Summary
• One way to secure network is to isolate segments
that have secure data transmission requirements.
You can segment network at Layer 3 using
routers and subnets and at Layer 2 using
switches and VLANs.
• Routers and firewalls can be used to screen traffic
that passes through screened subnet, with three
typical configurations: bastion host, three-pronged
configuration, or back-to-back configuration.
• To group computers in segments independent of
IP addresses, you can use switches to create
virtual LAN (VLAN). In VLAN, all communication
must pass through router.
Summary
• Two types of filters can add another layer of
protection: IP address filtering and IP packet
filtering.
• Data transmission protection protocols include
SSL, TSL, IPsec, SMB signing, and SSH.
• SSL and TLS: Protocols that provide session
encryption and integrity. TLS is enhancement of
SSL. SSL has two components: SSL Handshake
Protocol and SSL Record Layer.
• IPsec: Used to secure traffic on LAN or VPN.
Offers: Confidentiality, authentication, data
integrity, packet filtering, protection against data
reply attacks.
Summary
• IPsec includes two major security mechanisms:
Authentication header (AH) and Encapsulating
Security Payload (ESP).
• ESP can be used to provide confidentiality, data
origin authentication, data integrity, some replay
protection, and limited traffic flow confidentiality. It
can operate in one of two modes: Transport mode
or tunnel mode.
• Internet Key Exchange (IKE) protocol is used
with IPsec to create security associations (SAs) ,
provide entity authentication and secure
negotiation of all cryptographic algorithms.
Summary
• Server Message Block (SMB) signing adds
security (through keyed hash) to SMB
protocol.
• Secure shell (SSH) provides security,
public key encryption schemes for remote
login programs.
Key Terms
• 802.1Q
• Acknowledgement (ACK)
message
• Authentication data
• Authentication Header (AH)
• Back-to-back configuration
• Bastion host
• Broadcast domain
• ChangeCipherSpec
message
• Cipher spec
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ClientHello message
Countermeasures
Demilitarized zone (DMZ)
Denial of Service (DoS)
attack
Digital Signature Algorithm
(DSA)
Encapsulating Security
Payload (ESP)
Footprint
Gateway-to-gateway
security
Key Terms
• Half-open connections
• IKEv2
• Integrity Check Value
(ICV)
• Internet Key Exchange
(IKE) protocol
• IP address filtering
• IP packet filtering
• IPsec policy
• IP Security (IPsec)
• IP within IP
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Key block
MasterSecret
Next Header
Packet sniffer
Packet tampering
Padding
Pad length
Payload data
PreMasterSecret
Protocol data unit
(PDU)
Key Terms
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Remote shell (rsh)
Replays
RFC 2401
RFC 2402
RFC 2406
RFC 2409
RFC 4306
Screened subnet
Secure Sockets Layer (SSL)
Security Association (SA)
• Security Parameters Index
(SPI)
• Sequence number
• ServerHello
• Server Message Block
(SMB)
• Server Message Block
(SMB) signing
• SSH
• SSL Handshake Protocol
Key Terms
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SSL Plaintext records
SSL Record Layer
Switch
SYN message
Tag
TCP session hijacking
TCP SYN flooding attack
The wild
Three-pronged configuration
• Transport Layer Security
(TLS)
• Transport mode
• Trusted host
• Tunnel mode
• Virtual local area network
(VLAN)
• VLAN hopping
• VLAN ID
• VLAN
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